Celiac Disease Tests

Celiac disease tests are a group of assays developed to help diagnose celiac disease and a few other gluten-sensitive conditions. These tests detect autoantibodies that the body produces as part of an inappropriate immune response to dietary proteins found in wheat, rye, and barley (gluten and gliadin). In the past, the only way to diagnose celiac disease was by examination of a tissue biopsy of the small intestine. While this microscopic evaluation is still considered the gold standard and is still used to confirm a diagnosis of celiac disease, the availability of less invasive blood tests to screen for celiac disease has reduced the number of biopsies needed. Autoantibody blood tests that are available include:

Anti-tissue Transglutaminase Antibody (tTG), IgA: Tissue transglutaminase is an enzyme responsible for crosslinking certain proteins. Although “tissue” is in the name of this autoantibody, it nevertheless involves testing blood and not tissue since the autoantibody is found in the blood. A few laboratories also offer tests to detect IgG anti-tTg.

Anti-Gliadin Antibodies (AGA), IgG and IgA: Gliadin is part of the gluten protein found in wheat (similar proteins are found in rye, barley, and oats). AGA is an autoantibody against the gliadin portion.

Two other tests that are now rarely used:

Anti-Endomysial Antibodies (EMA), IgA: Endomysium is the thin connective tissue layer that covers individual muscle fibers. Anti-Endomysial antibodies are developed in reaction to the ongoing damage to the intestinal lining. It has been found that tTg is the substance detected in this test. Almost 100% of patients with active celiac disease and 70% of patients with dermatitis herpetiformis (another gluten-sensitive condition that causes an itchy, burning, blistering rash on the skin) will have Anti-EMA, IgA antibodies. The test is more difficult to do and interpret properly than anti-tTg.

Anti-Reticulin Antibodies (ARA), IgA: Anti-ARA is not as specific or sensitive as the other autoantibodies. It is found in about 60% of celiac disease patients and about 25% of patients with dermatitis herpetiformis.

Each of the celiac blood tests measures the amount of a particular autoantibody in the blood. For each test, both IgG (Immunoglobulin G) and IgA (Immunoglobulin A) antibodies can be measured; however, few laboratories offer IgG tests other than for gliadin. IgG and IgA are two of the five classes of antibody proteins that the immune system creates in response to a perceived threat.

In general, the IgA antibody is more specific for celiac disease (since IgA is the type of antibody made in the intestine) and is measured almost exclusively. IgG versions may be ordered either to complement the IgA testing and/or ordered because someone has an overall deficiency in IgA. This happens about 2% of the time with celiac disease and can lead to some false negative test results.

A blood sample is obtained by inserting a needle into a vein in the arm.